I've been fiddling with Photoshop during the last few days, looking for an easy way to create a photo mosaic. The idea was to divide a large image among a set of thumbnails, so that each of them contains a small portion and they all together make the original photo up. After a bit of trial and error, I finally got it. Here's how to create a photo mosaic in Photoshop, in just a few easy steps.

1. Open a blank image and fill in the background with any solid color - to work more comfortably. Then create a new layer, draw a square shape on it with the Marquee tool (M) and fill it with white.

2. Create another new layer and with the Marquee tool again, create another square shape inside the original one and fill it with black. You'll need to deselect (Ctrl+D) the previous one in order to be able to create this shape.

3. Go back to the first layer you created, and add a Drop Shadow effect to the white frame.

4. Now it's time to group those two layers together. Create a folder on your Layer window by clicking the highlighted button in the screenshot, and drag the layers onto it to store them inside the folder.

5. Here comes the fun part: duplicate the folder containing those two layers to create as many thumbnails as you need for your mosaic. In my case, 11 copies - plus the original folder - was enough.

6. Merge all the folder layers into one (you can easily achieve this by making all other layers invisible and going to Layer > Merge Visible). Then import the image you want to turn into a mosaic, and make this photo layer invisible as well.

7. Go to Select > Color Range and click on the black areas of your mosaic, so that only those black squares are selected.

8. Make sure the selected layer is the one with the squares, and while all those black areas are still selected, press the Del key. Your work should look similar to this:

9. Now click on the photo layer to make it the active one and go to Select > Inverse to invert the selection. Press Del again and you'll get rid of all the areas in the image that remain outside the squares.

10. Ta da! Your mosaic is done. You can keep the background layer or remove it if you prefer not to have any specific color under your photo composition.